This application claims the benefit of Korean Patent Application No. 2000-30189, filed on Jun. 1, 2000, under 35 U.S.C. xc2xa7119, the entirety of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a capacitor electrode of a storage capacitor for use in a LCD device.
2. Description of Related Art
In general, LCD devices have various advantages including being thin in thickness and low in power consumption, and so on, in comparison with CRT (cathode ray tube) display devices. Therefore, such LCD devices might be expected to be substituted for CRT display devices and have been a matter of great interest in some industry fields.
FIGS. 1A and 1B are schematic views illustrating a typical liquid crystal display (LCD) device. As shown in FIG. 1A, the LCD device 11 includes first and second substrates 5 and 22, and an interposed liquid crystal layer 14 having liquid crystal molecules therebetween. The first substrate 5 as an upper substrate includes a color filter 7 and a transparent common electrode 18 formed against the color filter 7. The second substrate 22 as a lower substrate includes pixel regions xe2x80x9cPxe2x80x9d, pixel electrodes 17 formed on the pixel regions xe2x80x9cPxe2x80x9d, gate lines 13 arranged in a transverse direction, data lines 15 arranged in a perpendicular direction to the gate lines 13, and thin film transistors (TFTs) xe2x80x9cTxe2x80x9d arranged near crossing points of the gate and data lines 13 and 15.
Each TFT xe2x80x9cTxe2x80x9d includes an active layer 36, a gate electrode 35, and source and drain electrodes 31 and 33. The gate electrode 35 contacts with the gate line 13 and the source electrode contacts 31 with the data lines 15. Also, the drain electrode 33 contacts with the pixel electrode 17. The pixel electrode 17, an insulating layer (not shown) and the gate line 13, which are stacked in the above-described order, form a storage capacitor (not shown).
Further, the storage capacitor may be formed by adding a capacitor electrode 37. In other words, as shown in FIG. 2, the pixel electrode 17, the insulating layer (not shown) and the capacitor electrode 37, which are stacked in above-described order, form the storage capacitor xe2x80x9cCxe2x80x9d. The capacitor electrodes 17 are equidistantly arranged in a direction parallel to the gate line 13.
FIG. 3 shows a conventional in-plane switching (IPS) type LCD device. As shown in FIG. 3, in the conventional IPS type LCD device, the pixel electrode 17 and the common electrode 18 are arranged on the same substrate, i.e., the lower substrate, and branches 17a of the pixel electrode 17 are interposed between branches 18a of the common electrode 18. Further, the pixel electrode 17, an insulating layer (not shown) and the gate line 13, which are stacked in the above-described order, form a storage capacitor xe2x80x9cCxe2x80x9d. When a voltage is applied to the pixel electrode 17 and the common electrode 18, a parallel electric field is formed. The parallel electric field operates liquid crystal molecules.
FIG. 4 shows a conventional LCD device having a storage capacitor shown in FIG. 2. The storage capacitor having a structure shown in FIG. 2 is formed on the pixel region and usually uses a separate capacitor electrode line to apply a voltage. A voltage that is applied to the storage capacitor is obtained by using a common voltage that is applied to the upper substrate or by supplying a separate capacitor voltage. The storage capacitor shown in FIG. 4 does not use a separate voltage and uses a common voltage as a capacitor voltage by connecting the capacitor electrode line with the common electrode line.
As shown in FIG. 4, the upper substrate 5 has a common electrode (reference 18 of FIG. 1), and the lower substrate 22 includes the gate lines 13 arranged in a transverse direction and the data lines (not shown) arranged in a direction perpendicular to the gate lines 13. The lower substrate 22 further includes the capacitor electrode lines 37 equidistantly arranged in a direction parallel to the gate lines 13. Both terminals of the capacitor electrode lines 37 are electrically connected with each other, respectively. The gate lines 13 are connected with a gate driver 57 transferring signals through a gate pad 41. The data lines (not shown) are connected with a data driver 59 transferring signals through a data pad (not shown).
The gate and data drivers 57 and 59, in FIG. 4 are mounted on the tape carrier package (TCP), and the TCP having the gate driver is referred to as a gate TCP and the TCP having the data driver is referred to as a data TCP. A capacitor voltage may be usually supplied through either the gate TCP or the data TCP.
In FIG. 4, a capacitor voltage is supplied through the data TCP. The gate line 13 has an electrostatic circuit 62 at an end portion opposite to the gate pad 41. Though the electrostatic circuit 62 is connected with the capacitor electrode line 37, the gate line 13 is electrically independent of the capacitor electrode line 37 under a normal condition. However, when an overcurrent flows along the gate line 13 due to the static electricity, the gate line 13 and the capacitor electrode line 37 are electrically connected with each other by a static electricity across the electrostatic circuit 62. As a result, an equipotential is formed between the gate line 13 and the capacitor electrode line 37, thereby preventing a line open of the gate line 13 due to the static electricity.
The capacitor electrode line 37 is electrically connected with dot patterns 63 made of Ag paste, which are located at four corners of the lower substrate 22 for connection with the common electrode (not shown) of the upper substrate. Further, the capacitor electrode lines 37 are connected with an auxiliary capacitor electrode line 38, which is connected with the data drivers 59 via connecting lines 39.
In a storage capacitor having such a capacitor electrode line 37, when a capacitor voltage is applied to the capacitor electrode line 37 through the data drivers 59 respectively arranged on upper and lower regions of the lower substrate 22, a current flows in two direction, i.e., from both end portions to a central portion. A capacitor voltage level gets to be lowest at a central portion of the capacitor electrode line 37 due to a line resistance of the capacitor electrode line 37, and therefore a gray level becomes lowest at the central portion of the capacitor electrode line 37, whereby a central portion of a screen looks white or dark. That is, display characteristics of the LCD device vary according to the pixel position on the pixel matrix being considered.
FIG. 5 shows the IPS type LCD device shown in FIG. 3. As shown in FIG. 5, common electrode lines 18 of the IPS type LCD device are arranged in a direction parallel to the gate lines 13 just like the capacitor electrode line 37 of the LCD device shown in FIG. 4. When a capacitor voltage is applied to the common electrode line 18 from the data drivers 59 respectively arranged on upper and lower regions of the lower substrate 22, a current flows in two directions, i.e., from both end portions to a central portion. A capacitor voltage level gets to become lowest at a central portion of the common electrode line 18 due to its line resistance, a gray level becomes lowest at the central portion of the common electrode line 18, whereby a central portion of a screen looks white or dark. That is, display characteristics of the IPS type LCD device vary according to the pixel position being considered on the pixel matrix.
In other words, in case of a normally white state that a screen shows a black state when a voltage is applied to the liquid crystal layer, since a low voltage is applied to the central portions of the capacitor or common electrode lines, a arrangement state of the liquid crystal molecules is unstable or abnormal so that a light leakage occurs, leading to a white screen in the central portion of a screen. Further, in case of a normally black state that a screen shows a white state when a voltage is applied to the liquid crystal layer, since a low voltage is applied to the central portions of the capacitor or common electrode lines, a arrangement state of the liquid crystal molecules is unstable or abnormal and polarization state is unstable so that an amount of light emitted to the outside is reduced, leading to a black screen in the central portion of a screen.
For the foregoing reasons, there is a need for an LCD device that does not have the lowest gray level at the central portion of a screen, i.e., improved display characteristics that do not vary according to the pixel position being considered on the pixel matrix.
To overcome the problems described above, preferred embodiments of the present invention provide a liquid crystal display (LCD) device having improved display characteristics.
A preferred embodiment of the present invention provide, in part, an LCD device that does not have the lowest gray level at the central portion of a screen i.e., that has display characteristics which do not vary according to the pixel position being considered on the pixel matrix.
In order to achieve the above object, the present invention provides (in part) a liquid crystal display device, including: a first substrate; a second substrate spaced from the first substrate, having gate lines arranged in a first direction, data lines arranged in a direction perpendicular to the gate lines, capacitor electrode lines arranged in a direction parallel to the gate lines, each of the gate lines having electrostatic circuits located on second end portions thereof, first end portions of the gate lines having pad portions, each of the capacitor electrode lines having electrostatic circuits located on second end portions thereof, first end portions of the capacitor electrode lines being electrically connected with each other; a liquid crystal layer interposed between the first and second substrates; gate driver units electrically connected with the gate lines through the pad portions of the gate lines; and data drivers units electrically connected with the data lines, wherein the electrostatic circuits of the gate lines electrically separate the second end portions of the gate lines from each other, and the electrostatic circuits of the capacitor electrode lines electrically separate the second end portions of the capacitor electrode lines from each other.
The second end portions of the capacitor electrode lines can be located opposite to the pad portions of the gate lines. The second substrate further includes pixel electrodes located on regions defined by the gate and data lines. The second substrate further includes insulating layers interposed between the capacitor electrode lines and the pixel electrode so that the capacitor electrode line, the insulating layer and the pixel electrode form a storage capacitor. The first substrate has a common electrode, and the second substrate has four dot patterns located on four corners thereof, wherein the four dot patterns are connected with the capacitor electrode lines and the common electrode of the first substrate. The dot pattern is made of Ag paste.
The present invention further provides (in part) a liquid crystal display device, including: a first substrate; a second substrate spaced apart from the substrate, having gate lines arranged in a first direction, data lines arranged in a direction perpendicular to the gate lines, common electrode lines arranged in a direction parallel to the gate lines, and pixel electrodes, the gate lines having electrostatic circuits located on first end portions thereof, second end portions of the gate lines having pad portions, the common electrode lines having electrostatic circuits located on first end portions thereof, second end portions of the common electrode lines being electrically connected with each other, the common electrode having branches, the pixel electrode having branches, the branches of the common electrode being equidistantly interposed between the branches of the pixel electrode; a liquid crystal layer interposed between the first and second substrate; gate driver units electrically connected with the gate lines through the pad portion of the gate lines; and data driver units electrically connected with the data lines, wherein the electrostatic circuits of the gate lines electrically separate the first end portions of the gate lines from each other, and the electrostatic circuits of the capacitor electrode lines electrically separate the first end portions of the capacitor electrode lines from each other.
The first end portions of the common electrode lines can be located opposite to the pad portions of the gate lines. The first substrate has a common electrode, and the second substrate has four dot patterns located on four corners thereof, wherein the four dot patterns are connected with the capacitor electrode lines and the common electrode of the first substrate. The dot pattern is made of Ag paste.
As described herein before, using an LCD device having a structure of a capacitor electrode line and a common electrode line according to the preferred embodiment of the present invention, since a gray level becomes lowest at the edge of a screen, display characteristics can be improved remarkably.
Advantages of the present invention will become more apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.